The present invention relates generally to venous cannulae and catheters to be used during a medical procedure. More specifically, the present invention provides an improved cannula that is expandable from a contracted condition to an expanded condition to allow greater fluid flow in a vessel.
A venous cannula is provided having an expandable scaffolding that is configured for optimizing venous drainage during a medical procedure. In the collapsed position, the cannula scaffolding has a low profile especially suited for ease of entry into a vessel. In the expanded or deployed position the cannula scaffolding increases radially creating an area of free space between the catheter body and the vessel to optimize the fluid flow capacity of the catheter. The venous cannula of the present invention may be inserted from a peripheral vein such as the femoral, subclavian or jugular vein or alternatively may be used from a central approach into the right atrium, the superior vena cava, inferior vena cava or both.
Over the past decades tremendous advances have been made in the area of heart surgery, including such life saving surgical procedures as coronary artery bypass grafting (CABG), cardiac valve repair or replacement and other surgical interventions. The development of cardiopulmonary bypass (CPB) has been a key technology making these advances possible. Performing heart surgery is a delicate operation requiring precise placement of sutures and incisions; therefore the majority of heart surgery is performed on an arrested or stopped heart. While the heart is arrested, systemic circulation is provided to the patient by using a cardiopulmonary bypass system or circuit. Typical bypass systems include: a venous cannula for withdrawing deoxygenated blood from the venous system, a venous reservoir for receiving the deoxygenated blood from the venous cannula, an arterial pump for circulating the venous blood from the venous reservoir to an integral heat exchanger and membrane oxygenator for conditioning the blood to the appropriate temperature and chemical composition and an arterial cannula for delivering the conditioned blood back to the patient. In addition, most extracorporeal circuits include a cardioplegia circuit or coronary circuit which performs the function of arresting the heart, as well as suction pumps for aspirating blood from the pericardial sac or in the pleural spaces through the use of a suction catheter, and/or to evacuate blood from the left ventricle by using a venting catheter.
Closed chest cannulation of the femoral artery and vein has also been practiced by physicians for the establishment of profoundly hypothermic total circulatory arrest and for reoperations with a high probability of entering a cardiac chamber during sternotomy. Even more recently, cardiac surgery has advanced to include a field of surgery called minimally invasive cardiac surgery. One specific type of minimally invasive cardiac surgery uses intercostal spaces to access a patient""s heart and supplies the systemic circulation with oxygenated blood by using cannulas introduced into peripheral vessels. These procedures have helped reduce hospital recovery time by eliminating the more traumatic median sternotomy incision that is used in traditional heart surgery. However, since the cannulas used in these surgeries have smaller outside diameters, designed to enable introduction into peripheral vessels, there is a corresponding reduction or decrease in fluid flow through the internal lumens of these cannulas.
In more traditional CPB circuits, physicians typically place the venous reservoir at an elevation below the patient so that venous pressure and gravitational siphoning draw fluid through the venous cannula into the venous reservoir. This is problematic especially when using the peripheral cannulation technique since the cannula is much longer requiring more pressure to provide adequate fluid flow through the cannula. A second problem associated with using gravity, or siphoning is that the venous reservoir is limited in placement below body level, therefore more tubing is required to remove the venous reservoir out of the surgeon""s way due to his location relative to the patient. This is disadvantageous since more tubing will require a larger amount of priming volume to fill the circuit which also clutters the surgical suite and makes the overall circuit less efficient.
Recognizing that gravity or siphon drainage may not always be sufficient to create adequate pressure for fluid withdrawal, especially in minimally invasive techniques, suction has been implemented as a means for increasing overall venous drainage. However, too much vacuum or suction results in the vein being collapsed down around the cannula shaft rendering the fluid drainage ports incapable of providing a passage way for fluid flow.
Another way physicians have tried to increase fluid flow through is to increase the diameter of the venous drainage cannula. One disadvantage to this solution is that a larger cannula shaft takes up more space in an already crowded surgical field and does not resolve the issue of minimizing priming volume. In addition, cannula size is limited in applicability based upon individual anatomy and the diameter of the vessel into which the cannula is to be inserted especially when using peripheral cannulation. Furthermore, cannulae having sufficient internal diameter to draw adequate blood flow are either so thin-walled that they are prone to kinking and collapse or are so thick-walled that they are not very flexible and have an overall diameter that is too large to be easily inserted into a peripheral vein.
Therefore, what has been needed and heretofore unavailable is a venous return cannula with a vacuum-controlled small reservoir or a special system that incorporates direct pumping from the venous cannula. Such a system creates a more compact circuit, requires less priming volume and is able to be located at the level of the operating table near the head of the patient. Furthermore, it would be advantageous to have a venous cannula that can be inserted either peripherally or centrally into the venous system of a patient at a minimum diameter that is capable of expanding to provide maximum fluid flow. The present invention solves these problems, as well as others.
In keeping with the foregoing discussion the present invention provides a venous drainage cannula for cardiopulmonary bypass that prevents vena cava collapse which can interfere with efficient venous drainage. The cannula of the present invention is useful for standard gravity drainage or vacuum assisted/suction drainage. The cannula of the present invention has a flexible shaft composed of a proximal tubular body and a distal expandable scaffolding. The expandable scaffolding has a contracted position, facilitating insertion into a vessel and an expanded condition configured for supporting the vessel to allow optimal flow. The cannula is inserted into a vessel and navigated into an operative position within the patient""s venous system. Once the cannula is in the proper position, the scaffolding is expanded either through passive, active, mechanic, hydraulic, pneumatic, thermal or electrical actuation. The cannula of the present invention is capable of expanding a collapsed vein to its normal diameter and/or capable of supporting the vein when suction is applied to the cannula to help increase fluid flow through the cannula. Unlike conventional venous cannulae, whose drainage ports can become occluded when a vein collapses around the shaft, the cannula of the present invention has a scaffolding or permeable portion, which supports the vessel while suction or vacuum is applied to the venous cannula, and the drainage ports do not become occluded.
In a first illustrative embodiment, the venous cannula of the present invention has a cannula shaft with a tubular body, a scaffolding coupled to a distal end of the tubular body and an actuating member configured for expanding the scaffolding radially. The actuating member of this illustrative embodiment is in the form of a movable rod. To place the scaffolding in the contracted or insertion position, the actuating rod is moved in a distal direction contracting the scaffolding inward. To expand the scaffolding, the rod is moved in the proximal direction urging the scaffolding outward.
Coupled to the proximal end of the scaffolding is a tubular member having a proximal fitting coupled to a connection tubing in fluid communication with an extracorporeal circuit. In the expanded condition the scaffolding is sized and dimensioned to support the lumen of a vein allowing maximum diameter and flow of fluid into the tubular member and thereafter to the extracorporeal circuit. In addition, when necessary the scaffolding is designed to engage the vessel wall helping to keep the vessel in its natural condition when vacuum is applied. Alternatively, the expanded diameter of the scaffolding may be smaller than the vessel but is sized and dimensioned to keep the vessel from contracting beyond a certain diameter due to the rigid yet flexible characteristics of the scaffolding.
In a second illustrative embodiment, the venous cannula of the present invention has a cannula shaft with a tubular body, a shape memory scaffolding coupled to the distal end of the tubular body and an actuating member in the form of a movable sleeve. The sleeve is placed over the tubular member and the shape memory scaffolding to preloaded the scaffolding into the low profile insertion position. When the cannula is in the operative position, the sleeve is moved in the proximal direction, releasing the scaffolding, which automatically expands radially due to the shape memory properties of the scaffolding.
In a third illustrative embodiment one or more filament(s), wire(s), or strand member(s) are helically wound around the catheter to create an area of free space between the catheter and the vessel wall. The strand member is fixed at a distal portion of the tubular body. When the expandable venous catheter is placed in the operative position the proximal end of the strand member is advanced in the distal direction, urging the outward expansion of the strand member from the tubular body. The strand member can have a predetermined expansion diameter or alternatively may be configured to expand to a size equal to the internal surface of a vessel wall creating an area of free space between the tubular body and the vessel wall so that the ports do not become occluded by the vessel upon the application of suction.
In a fourth illustrative embodiment, the expandable scaffolding is comprised of supports, wings, standoffs, cones, or ribs, which are expanded by means of fluid inflation.